Mars City: Union Aerospace Corporate Division

"Marine? I can't believe you're still alive."

- Sergeant Kelly

Mars City: Union Aerospace Corporate Division is the third level of Doom 3. It is the same area as Mars City, but takes place after the demonic invasion. The marine is given his mission to link up with Bravo Team in this level. This is where the demo ends. Z-Secs equipped with machineguns are first encountered in this level, and it is also the first level in which a sentry bot engages in combat.

Summary


The marine returns to Mars City to find the place in chaos. The sounds of battle can be heard coming from the walls, but at this point most of Mars City has already fallen.

Fairly early in the level the marine encounters a survivor Roland who is hiding in the ventilation shaft near the elevator. Roland extends a ladder allowing the player to climb into the shaft. He then urges the marine to go get help.

The marine uses the ventilation shaft to enter the Manifest Control Office and from there fights his way through Security Operations to the Infirmary. From there he gains access to Marine Command and arrives back at Marine HQ. All the marines stationed there are dead, but a communications console is still working and has an incoming transmission from Sergeant Kelly who is pleasantly surprised to see that the marine is still alive.

Sergeant Kelly informs the marine that he is trapped in the Delta Complex and has decided to set up a command post there. He orders the marine to link up with Bravo Team and help them send a distress call to the Earth Fleet. In order to reach Bravo Team, the marine must head through Alpha Labs. Kelly also updates the marine's security clearance, giving him access to the ACO section of Mars City.

With the aid of a surviving sentry bot, the marine fights his way through the ACO area to the elevator. From there, he rides the elevator to the next level: Administration.

Areas

 * Elevator
 * Maintenance
 * Ventilation Shaft
 * Manifest Control Office
 * Manifest Control Entrance
 * Reception Processing
 * Conference Room
 * Hallway
 * Sec Ops Processing
 * Security Operations
 * Sec Ops Junction
 * Infirmary Access Junction
 * Operations Station
 * Infirmary
 * Infirmary Observation Room
 * Marine Command
 * Combat Preparation
 * Marine Headquarters
 * Marine Command Access
 * Command Access Junction
 * Common Area
 * Restroom
 * Central Access
 * Central Access Junction
 * Mars City Reception
 * ACO Access Junction
 * ACO Offices
 * ACO Lift Junction
 * Service Access

Objectives

 * Marine Comm Center
 * Return to the Command Message Center for a status update from Sergeant Kelly


 * ACO Keycard
 * Obtain an ACO Key card for access


 * Alpha Labs Administration
 * Join up with Bravo Team in Alpha Labs. Go through Administration for entry into the Alpha Labs Sector.

Characters

 * R. Roland
 * Sergeant Kelly
 * UAC announcer
 * Specialist Wilson (voice only)
 * S. Holmes
 * Sentry Bot

PDAs

 * Marcus Stanton: Found in Manifest Control Office
 * Marcus Caseon: Found in Infirmary.
 * Bill Tyson: Found in Marine Command, in corridor behind flaming pipe.
 * Duncan Mathews: Found in ACO Lift Junction. Requires going through a service access on the right of the room.

Enemies
Note: Includes only enemies that can be fought and killed. The enemy count on Nightmare is the same as on Veteran. There are no changes in the enemy amount in the BFG Edition.

Items
The item count on Nightmare is the same as on Veteran, except the med kits are absent. There are no changes in the amount of items in the BFG Edition. There's also one health station on the level, with 100 health in reserve.

Starting inventory
If the player starts the level via a console command, they will start with these items:

Locker/door codes
For the sources of the codes, see Doom 3 locker codes.
 * Storage locker #017 - Supplies: 347. Contains: med kit (large), security armor, clip (small), shells (small) x2.
 * Weapons Storage: 584. Contains: shotgun x2, machine gun x2, clip (large) x2, shells (small), med kit (large), security armor (2 on Recruit, 1 on Marine/Veteran).

Secrets

 * In the starting room there's a machine gun and some shards lying on a catwalk from which the player came from in the intro, but the staircase has collapsed so the player has to jump on a railing to get there.
 * When the player first meets the sentry bot, one can go back to reception where they got the PDA at the start of the game. There, one can access a nearby room with supplies by jumping through the window with missing glass panel.
 * In the last room, with the exit elevator in it, there's an vent shaft to the right from the entrance that can be used to access the second floor of the room, which contains a PDA that can be used to gain access to a locked office right before the elevator room, and some supplies.

Trivia

 * On the original Xbox version of the game, the level is divided into two parts: Mars City - South Side and Mars City - North Side.
 * In Sec Ops Processing the player can choose to go to Security Operations through a small corridor. If the player does that they will encounter two Z-Secs and, among other things, a non-functioning door. However, if the player chooses not to go there, later on when they reach Marine Command Access, the same door will be blown from its frame and the same Z-Secs will attack the player anyway. However, the player will encounter an additional Z-Sec if they enter Security Operations this time.
 * If the player chooses not to go to Security Operations and proceeds to Infirmary Access Junction and then backtracks, on Marine skill level and above, an additional Z-Sec will spawn and ambush the player.
 * In Infirmary where you get attacked by the unique morgue zombie, if you kill said zombie before it manages to get up from its bed, the one or two (depends on the skill level) machine gun Z-Secs won't spawn. This is likely a bug, as it seems the trigger for the Z-Sec(s) to appear is scripted to work after the morgue zombie's get up sequence is finished.
 * If the player goes to Combat Preparations (armory) room before getting the transmission from Sarge, a Z-Sec will be waiting inside.
 * If the player lingers in the common area by the kitchen for a while (around ten seconds) two Z-Secs will appear in the corridor and attack.
 * If the player go into the bathroom and look at themself in the mirror, they will see a vision of marine turning into a zombie. When the vision ends, an imp will spawn outside.
 * In the demo version, when the level is completed, the player's vision will turn red and evil laughter will be heard.
 * In the original release of the game, when the player arrives at the front of the Marine HQ, the female UAC facility voice can be heard saying "Video link-up requested" repeatedly until the player approaches the communication console. In the BFG Edition, this voice line is missing.